Here in Brazil, we have the CPF (somewhat equivalent to US SSN), a "unique" number assigned by the government for identification. It's used by almost every busi

Here in Brazil, we have the CPF (somewhat equivalent to US SSN), a "unique" number assigned by the government for identification. It's used by almost every business I have ever know as a key. Not always primary key, but certainly people treat it as unique. Except for the fact they are not unique, and there have been cases where people from different states have the same number because each state generated this "random" number, but didn't actually check with each other if it's really unique. It is legally enforced, no two people should ever have the same, but they do. The only way to have uniqueness is if you know the algorithm AND can control that it behaves as expected. Anything else is just kidding yourself.